Protein kinase C interacting protein (PKCI/HINT1) is a small protein belonging to the histidine triad (HIT) family of proteins. Postmortem studies have identified PKCI/HINT1 as a candidate molecule for schizophrenia and bipolar disorder. In studies from our laboratory, PKCI/HINT1 KO mice displayed a phenotype of behavioral and endocrine features which indicate changes of mood function, including anxiolytic- like and anti-depressant like behaviors and supersensitivity to amphetamine. These results suggest that PKCI/HINT1 plays a key role in normal CNS function and state of mental diseases. The present R21 proposal is designed to set the groundwork for long-term studies characterizing the function of PKCI/HINT1 at the cellular level and developing novel inhibitors of the protein to facilitate the characterization as well as have the potential to be developed into novel therapeutic agents for related CNS disorders. The specific aims include: Aim 1. Develop cellular assays for PKCI/HINT1 focusing on potential activities associated with neuronal survival, neuronal growth and calcium signaling. Assay development will emphasize high- throughput capabilities to facilitate future drug discovery and optimization efforts. Aim 2. Identify low molecular weight compounds with a high probability of binding to PKCI/HINT1 using structure-based computational drug design methods. Identified compounds will then be assayed for their ability to bind PKCI/HINT1 using in vitro fluorescence and ITC assays, supplemented with NMR analysis. In essence, the proposed work will fill a gap between the known 3D structure of PKCI/HINT1 and its known in vivo behavioral characteristics. Knowledge of the cellular function of PKCI/HINT1 gained in the proposed study will fill this gap allowing for extensive future studies of the pharmacology of PKCI/HINT1, potentially leading to a rational drug design approach to the development of novel therapeutic agents for mood disorders.